6 week old boy. For about 1 week, the parents noticed a hard, painless, non-warm swelling of about the size of a walnut on the right side of the neck.Patient history includes: Cesarean section due to breech position, otherwise unremarkable. Head position tends to be more to the left, although movement is unremarkable.

Pathomorphology or Pathophysiology of this disease :

The cause of sternocleidomastoid pseudotumor of infancy is unknown. The old name, "Head-nick hematoma" refers to the original idea that the this tumor was caused by trauma to the sternocleidomastoid muscle during birth. Often, one finds a difficult delivery (vacuum extraction or forceps) in the history. In the typical case, 2-4 weeks after birth, the child develops a hard, painless nodule in the region of the middle sternocleidomastoid muscle. The right side is more often afflicted than the left. A bilateral sternocleidomastoid pseudotumor of infancy is extremely rare. Biopsies (which typically should not be necessary) show spindle-like fibroblasts next to atrophic muscle cells and a low-grade inflammatory response can also be seen.

Radiological findings:

Ultrasound 1: In the panorama-view (transversal neck soft tissue at the level of the thyroid isthmus), one sees an obvious thickening and structural changes of the right sternocleidomastoid muscle in comparison to the opposite side.

Ultrasound 2: Longitudinal: The sternocleidomastoid muscle in comparison. Right - obvious spindle-like thickening of the sternocleidomastoid muscle with inhomogenic structure and some echogenic areas.

Ultrasound 3: Sternocleidomastoid muscle transverse: comparison.

Ultrasound 4: Transverse section of the right sternocleidomastoid muscle .

Ultrasound 5: In the color doppler examination, the inhomogenic perfusion within the thickened muscle is seen.

Ultrasound 6: Follow-up ultrasound one month after the initial examination. Longitudinal images. The thickened right sternocleidomastoid muscle has regressed.

This is a non-neoplastic cervical mass, which is seen for over the course of a few months. Spontaneous regression is expected. The incidence is, according to literature, about 0.4%. In about 20% of the patients, a torticollis develops. Treatment: symptomatic, physical therapy with careful exercises to stretch the neck musculature.